Casing is used in oil and gas well construction. In certain applications a string of casing may be deployed using a work string, for example, drill pipe, so that the casing string does not extend all of the way back to the drilling rig. These scenarios can include a liner and a sub-sea casing longstring.
A longstring is a string of casing whose upper end extends up to the wellhead. So a longstring used on a sub-sea well is one that does not extend up to the drilling rig once installed but whose top resides in the sub-sea wellhead which sits on the sea floor. A liner is a string of casing whose top end resides within the length of a previously installed casing string. The top end of a liner does not reside at surface or within a wellhead.
Both of these scenarios utilize drill pipe in order to deploy the casing string. It is known in the industry that the deployment a casing string may exert excessive pressure on an open formation. The excessive pressure may overcome the strength of the formation and thus cause the formation to break down and cause a cement job. Surge reduction tools exists that when used in conjunction with auto-fill float equipment allow the fluid that is being displaced from the well bore to move up the inside of the casing and deployment string, thus reducing the surge pressure. Specifically, the surge reduction tools divert fluid flow from the inside of the deployment string to the annular space above the casing string. Once it is determined that casing string must be washed down and or cemented then surge tool is closed so that the fluid flow is no longer diverted to the annular space above the casing. Reliable closing of the flow diversion is critical for ensuring successful cementing operations.
With the onset of dual gradient drilling methods a need exists which will require that a surge reduction tool begin in the closed position until it is deployed below the sea floor, then be allowed to open to allow fluid diversion from the inside to the annulus, and then be closed again to allow wash down or cementing operations.
It is possible that other applications may exist for this type of tool. It is also possible that applications exist requiring a tool to be opened and closed multiple times.
The present invention incorporates multiple shifting sleeves controlled by pressure enabled by sealing balls or plugging devices that land on seats and which shift the tool into an open or closed position. The seats then allow the ball or plugging device to be released through the tool. Proper sizing of the seats for balls or other plugging devices allows selective opening and closing of the tool, as well as allowing for a multi-stage tool that may be opened and closed repeatedly.
Additionally, the invention may incorporate a test sub that allows the work string to be pressure tested after the tool is closed, providing a positive indication to the surface that successful closure and sealing has occurred, and that further operations may proceed.